Many fluid control valves utilize axially shiftable spools to direct fluid to radial ports of a valve bushing; the edges of valve spool lands coact with the ports in a manner well known in the fluid control arts. Precise correlation between port spacing and land edge spacing is usually not a problem, since many spools do not perform a metering function and are simply fired quickly by a solenoid operator to uncover a port.
In flow metering valves, e.g., servo valves and deceleration valves, where precision mechanical movements must translate to exact flow requirements, and vice-versa, problems can arise if the exact connection of a land with a port is not predictable.
Several prior art U.S. patents have dealt with attempting to construct valve bushings in a manner controlling port spacing and port cross section:
U.S. Pat. No. 3,103,739, of W. C. Moog, Sep. 17, 1963, teaches machining squared port notches across the ends of bushing sections, sizing the overall length of the discrete sections, serially stacking the bushing sections, and brazing the assembled sections together to create a unitary bushing.
U.S. Pat. No. 3,353,249, of C. E. MacFarlane et al., Nov. 21, 1967, teaches forming of bushing sections by sintering metal, forming port notches across the ends, and adhesively bonding the sections together to create a unitary bushing.
U.S. Pat. No. 3,885,284, of W. L. Clippard, III, May 27, 1975, teaches assembling separate sleeve components within a manifold cavity, for supporting an axially shiftable spool, and securely maintaining the sleeve components in an axially spaced relationship to create an annular gap between one another.
Another prior art U.S. patent has dealt with attempting to create a low cost valve spool with modular components:
U.S. Pat. No. 3,206,837, of S. H. Holmes, Sep. 21, 1965, teaches a method of manufacturing a reciprocal four-way spool valve, wherein discrete annular segments are assembled onto a mandrel, or core. The core has a head at one end and threads at the other, so that assembled segments can be rigidly maintained in position on the core, and thereby create a unitary valve spool. The valve housing is made of discrete plates, interlaminated between the spool segments and rigidly held together. The spool meters oil across the disc faces.
The forgoing patents teach relatively complex valve construction techniques which are obviated by the present invention.